function Vue(options){
    this._data = options._data

    for (let key of Object.keys(this._data)) {
        Object.defineProperty(this, key, {
          get() {
            return this._data[key];
          },
          set(newVal) {
            this._data[key] = newVal;
          },
        });
      }
}



//实例化Vue
const vm = new Vue({
    data: {
      count: 1,
      course: {
        type: "easy",
        name: "vue",
      },
    },
  });
  
  console.log(vm);